Multiple tube gas triode inverter



O Nov. 6, 1.151 c. c. SHUMARD 2,574,068

MULTIPLE TUBE GAS TRIODE INVERTER Filed Feb. 27, 1948 2 Si-lEETSSI-IEET l 1300 PERIOD 1 PERIOD 2 Pf/f/OD 3 Pf/9/0D4 FEW/0D 6 1100 e x F 2 moo I GHOU/VD 0 37 67 wt 1 arr/-16 04pm:

INVENTOR (L. ATTORNEY Nov. 6, 1951 c. c. SHUMARD MULTIPLE TUBE GAS TRIODE INVERTER 2 SHEETS-SHEET 2 Filed Feb. 27, 1948 INVENTOR CZdPZeJ C e/Zzzmard ATTORNEY Patented Nov. 6, 1951 MULTIPLE TUBE GAS TRIODE INVERTER Charles C. Shumard, Moorestown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 27, 1948, Serial No. 11,811

1 Claim. 1

This invention relates to improvements in electronic apparatus for inverting direct current into alternating current. More particularly, it relates to improved apparatus and methods for performing the inversion at high audio frequencies.

Although apparatus utilizing gas discharge tubes has been previously devised for changing D.C. to A.-C., this has generally been limited to frequencies of the order of a few hundred cycles per second and has been able to handle only low currents at relatively high audio frequencies. By utilizing the apparatus and methods of the present invention, alternating current outputs of 20,000 cycles and beyond may be accomplished using well designed tubes. Power output can be kw. or better.

In general, the improvements of the present invention are brought about by using two or more pairs of gas discharge tubes. Each pair of tubes charges and discharges a separate capacitor connected in interrelated anode to cathode circuits of the tubes and the outputs of these circuits are coupled to the load. The tubes are fired in an order such that each tube has time to deionize sufficiently before being readied to fire again and is maintained in such condition that it cannot fire prematurely while undergoing deionization.

The principal object of the present invention is to provide an improved method and apparatus for inverting direct current to alternating current, using at least four gas discharge tubes.

Another object is to provide improved means for inverting high amperage direct current to alternating current at high efficiencies.

Another object is to provide apparatus for inverting direct current to alternating current in which the efficiency of gas discharge tubes hav ing a certain deionization time is increased. 7

Still another object of the-present invention is to provide apparatus for inverting direct to alternating current in which at least four gas dis charge tubes are used but in which the power rating of each tube may be correspondingly lower than in a circuit utilizing two tubes.

These and other objects will be more readily apparent and the invention will be better understood from the following specification taken in connection with the drawings, of which:

Fig. 1 is a schematic diagram of a circuit representing one embodiment of the present inven- .tion,

Fig. 2 is a graph showing voltage wave forms in different parts of the circuit of Fig. l, and

Fig. 3 is a schematic diagram of a circuit of another embodiment of the present invention.

Referring to the embodiment illustrated in Fig. 1, a pair of gas discharge triode tubes l and 3 and a similar pair of tubes 2 and 4 are each provided with similar external grid circuits and similar external anode to cathode circuits. Tube I of one pair and corresponding tube 2 of the other pair are each provided with similar grid bias supplies 5 and 6, respectively, which normally furnish a negative bias to the grids of the tubes. Tubes 3 and 4, the other corresponding tubes of each pair, are provided with a common grid bias supply 1 similar to bias supplies 5 and 6 for furnishing normally negative bias to the grids of these tubes. However, the positive side of this common bias supply is grounded. This is in contrast to the other two which are isolated from ground.

Similar grid current limiting resistors 8, 9, It and H are provided in the grid circuits of the tubes I, 2, 3 and 4, respectively.

The output of a pulser timing unit (not shown) is connected to the grid of each tube through the transformers l2, l3, l4 and I 5, respectively. This pulser timing unit may be of any suitable conventional type such as shown in United States Patent 2,146,862 and the operation is as shown and described in co-pending application, Serial No. 725,249, filed January 30, 1947.

The cathodes of each of the tubes 1 and 2 are connected to the positive side of the grid bias supplies 5 and 6, respectively. The cathodes of each of the tubes 3 and 4 are connected to ground.

In the anode to cathode output circuits of tubes I and 3 is a common capacitor l6. Similarly, for the other pair of tubes 2 and 4, there is provided a like capacitor ll. The anode to cathode circuit path of tube I comprises an inductor 18, the B supply 22 and through ground to the capacitor l6, primary 23 of a loading transformer 21 and thence to the cathode.

The anode to cathode circuit path of tube 3 comprises an inductor 20, the primary winding 25 of loading transformer 21, the capacitor [6 and thence through ground to the cathode.

The first tube 2 of the second pair has an external anode to cathode circuit path exactly simi lar to the corresponding tube I of the first pair. It includes an inductor 19, the B supply 22, and through ground to the second capacitor ll, through the primary winding 24 of loading transformer 2! and thence to the cathode.

The anode to cathode circuit path of tube 4 is exactly like that of corresponding tube 3 of the first pair. It comprises an inductor 2|, the primary winding 26 of the loading transformer and through the capacitor I? to the grounded cathode.

The direct current source or B supply 22, which is to have its output inverted to A.-C., has its positive side connected to the anodes of both tubes I and 2 through the inductors I8 and 19 while its negative side is grounded.

As previously noted, a; primarywinding of loading transformer 2? is included in the anode to cathode circuit of each tube. These windings are all in the same direction, with the connections as illustrated, and provide couplingbetween the circuits. The transformer is provided with a common secondary winding Which-in turn is connected to the load as represented by 'loadxresistor 29.

The manner in which this circuit operates in inverting D.-C. from the B'supply '22'to A.-C. will now be described in more detail. 1 Let it' be assumed, at first, that all of the gas discharge tubes are non-conducting butheatedsand: ready lior conduction. Let tube- I be triggered Joy. the signal supplied .from the ;.pulser timi-ng -.unit through transformer I2. This is accomplishedby momentarily. making the grid more positive. than thecathode. Tube I -WHIJlOW conduct .and

capacitor I6 will" be charged from the .fB supply .through the inductor I 8 and theprimary winding .23 of transformer 21. Since no other circuit paths areavailableat the instant,-cap,acitor= l 6'Wi11 charge to. a voltage dependingzon. the constants of, the circuit. IIIhSllCh: an oscillatory circuit. hav- King; L, C and .R in: series with a: suddenlyappl-ied voltage 1 E, the -.maX-imum voltage ecmax. across the capacitor, if.no.originalzcharge-was ch -it, rises to a-value- :where 56? and If 0:0, corresponding to zero "resistancezthe voltage will rise to a value of'ZE, the theoretical but practically-unobtainable maximum value.

The capacitor would'then .start'to discharge causing current tojfiow inthe opposite direction but since the discharge tube conducts in only one direction, thecapacitor cannot discharge an'dis ,left. charged to acertain degree.

Since the currentcannot reverse its direction 'throughthe discharge tube, this tube will.now start to ,deionize. The deionization process'normally takes anappreciable interval of timebut 'may be hastened. The slower-moving :positive ions may be attractedjmore rapidly to the grid if the high negative "bias is immediately: returned .to this element afterthe tube is fired. "'Theitime constant of the grid circuit likewise "should be made .as low as feasible; hence, the value "of" the resistor 8;shoul,d'be;kept low and-the leakage reactance of the transformer I2 small. *Itis preferable to use a'regulated grid biassupply.

The resistance 8*may be made small although it is desirable'to limit grid'current flow while the the second pair is triggered through its pulsing transformer I3. p'acitor H, which ispreferabl'y equal in value This'charges the second cato capacitor I6, through-current,flowingin"the tube 2, inductor I9 and primary winding 24 of transformer 21. The current in the load resistor 29 will again be in the form of a damped halfcycle sine wave and will be of opposite polarity to the preceding half-cycle if caused to flow through primary winding 24 in a reversed direction since all primary windings of the load trans- ;former'are wound in the same direction. Thus,

-a"full=cycle partially damped sine wave is ob- 19 tained while capacitors I6 and I! are being :charged.

Another full-cycle of output current and power is obtained by consecutively firing the correspondi ingother two tubes, one being in each pair. First,

.15 thetubeS-is fired so that the first capacitor I6 discharges'throu'gh the path constituted by the .primary winding 25 of the loading transformer 21, inductor 20 which is similar to inductor I8, andtheitube 3. Then, after this half-cycle is 20 completed, the corresponding tube 4 of the other .pair is'firedsothat thesecond capacitor is discharged through the path comprising :the -primary winding 26, inductorl2l, which-is-also equal to inductor I8, and the tube-4,. itself.

It is only necessary, to properly select-thecircuit \constants so that the, first tube I is deionizing @during'thaduration of time .of charge of the second capacitor I'I. This time intervalis relatively large compared with "the timenecessary 39 to completely deionize tube i. The values o-f=L.-C ..and .R. may, therefore, I be adjusted to give oha-lf sine waves of relatively? short duration, thereby increasing the :output frequency. This is ca .marked radvantage 10f the apparatus .of :the present invention.

When steady state-operation-has been reached, thefinal voltageacrosseither capacitor I6 or I! is not the sameaas. thatat theendtofeachinitial .half-cycle when the :circuit-isfirstset in opera- .g .1 tion. Forsteady state operation, thefinal voltfageswand currents in .otherpartsof'the :circuit .are; also difierent from the initial ones..

Since the-operation-of the device is'zmainly concernedwithsteady state operation, the instantaneous conditionsof the principal circuit'ele- 'ments during variouspartsofa complete cycle of operation will beexplained with the a-idofthe .family of curves-shown in Fig. 2.

In.Fig. 2 areshown. voltages to ground at indicated points onv Fig-1. An essential point in obtaining the-increase of frequency possible with-a -four tube inverter .as comparedto a two -.-tube inverter. is thattheconstants be. so selected that the cathode voltage an on-tube I be maintained m positive with. respect to the plate voltageczg on this tube after tube I has conductedand starts-to deionize. Likewise,-cathode voltagesex e1 and ex, mustbe maintainedpositive, respectively,

with respect to..cP ,.c1: and e aftertubesl, 3 and .4,.respectively, have conducted andhave startedtodeionize.

Those-conditions will be obtainedif Otherwise, the voltages induced through the To transformer-back into "the cathode and "anode circuits will be of sufiicient magnitude that the conditions described above do not hold. The values of a andd used in obtaining-the'curves of Fig. "2 are a=0.25 and d=0'.0 In Fig. 2, 'five consecutive conducting-periods are shown,afte'r the-inverter circuit has reached the steady state voltages. of operation. Period 1 is fort tube I conducting, period 2, for tube 2, etc. is a repeat of period 1, for wt=41r radians later.

Although the curves of Fig. 2 are largely self- Period 5 capacitor remaining discharged. After this, the "entire operation repeats.

' It has'already been pointed out that the cathode voltage on any tube must be maintained positive with respect to its anode voltage after a tube has fired and been shut off. This condition must be maintained until the tube has deionized sufiiciently so that it will not conduct when the cathode potential is more negative than the anode potential until the grid potential is raised sufficiently positive to trigger the tube. This may be traced for any of the tubes and the potential changes on the other circuit elements may be explained as follows:

First half-cycle: Tube l is conductingother tubes nonconducting. The capacitor I6 is being charged such that point a is positive.

The anode and cathode potentials ee and (3x rise in a manner corresponding to the charge a on the capacitor IS.

The anode of tube 2 is at EB potential. The "potential 61;, on the cathode of tube 2' is highly "negative since its potential depends on the charge on capacitor [1 and its potential is still more negative due to potential induced in the primary winding 24 by current flowing in primary winding 23. The potential eP of the anode of tube 3 rises due to rise of potential on capacitor l6 as that -'.capacitor is charged. It is not identical with the potential on the capacitor since part of its potential is due to voltage being induced in primary winding 25 by current flowing in winding 23. The potential ea, on the anode of tube 4 rises and falls due to potential induced in the primary winding 26 by the currentfiowing in primary winding 23. Its potential is the algebraic sum of the potential on capacitor I! and the induced-voltage in the winding 26.

Where the potential of capacitor I1 is mentioned, there is meant the potential at point a! Second half-cycles Tube 2 is conducting, the ca- .pa-citor l6 remains charged, capacitor I! is being charged and currentflows in primary winding 24.

The potential cp on the anode of tube I drops to the B supply voltage, Es.

The potential cm is now the algebraic sum ofthe potential on the capacitor l6 and the voltage induced in the primary winding 23 by current flowing in the winding 24.

The potential cp is the algebraic sum of the charge on capacitor l6 and the potential induced in winding 25.

The potential 612, first of all, drops from Eato the same potential as that on capacitor l1, less tube drop, and then rises as the capacitor I7 is charged. It falls to EB as this half-cycle ends.

The cathode potential ex, also rises as capacitor I! is charged, its potential differing from that on the capacitor by the voltage induced in primary winding 24.

The plate potential cs also rises as capacitor I! is being charged but is not identical therewith because of the voltage induced in primary winding 26.

Third half-cycle: Tube 3 is conducting, the first capacitor I6 is discharging, the second capacitor ll remains charged, and current flows in the primary winding 25.

cp remains at Es potential.

er: drops because capacitor 16 is dischargin but is not identical with potential at point a because of induced voltage in primary winding 23.

c drops to and remains at EB potential and differs from the voltage on capacitor I! by the voltage induced in primary winding 25.

eg is the algebraic sum of the charge on the second capacitor I1 and the induced voltage in the primary winding 24.

8P3 drops to a potential almost equal to ground potential, being above ground only by the amount of the potential drop in the tube 3.

as, is the algebraic sum of the potential on the second capacitor I l and the induced voltage in the primary winding 26. Its wave form is opposite to that of 6x2 because the voltages are induced in opposite directions in the windings 24 and 26.

Fourth half-cycle: Tube 4 is conducting, the first capacitor l6 remains discharged, the second capacitor I1 is discharging, and current flows in the primary winding 26.

ex is the algebraic sum of the potential on capacitor l6 and the voltage induced in the primary winding 23.

en remains at EB potential.

ex, drop-s due to discharge of capacitor l! but the potential differs from that on the capacitor due to voltage induced in primary winding 24.

er remains at EB potential.

e1: first drops to the potential of capacitor l6 but throughout this half-cycle its potential is equal to the algebraic sum of the potential on capacitor l6 and the voltage induced in primary wind- 1 ing 25.

en, drops almost to ground potential, remaining above it only by the amount of potential drop in tube 4.

Throughout the operation, cathode potentials ex and ex, remain at ground since the cathodes of tubes 3 and 4 are grounded. V

. It will be noted that the potentials of the elements of the circuit associated with tubes l and 2 vary in a similar manner although separated by one-half cycle, while the potentials of the circuit elements of tubes 3 and 4 are also similar to each other in their variation.

An example of the selection of suitable circuit constants for a four tube circuit will now be given.

Example As a complete example of the selection of the circuit constants, take the values of EB=500, a=0.25 (m:.456) and d=.02 as limiting the peak forward or inverse voltage Em between the plate and cathode of tube Vs (or plate and cathode of I V4) to approximately, 1200 volts. The relation :aewocs between d;he2peak;-mverse voltage :E obtainedzand .The .relationbetweenlc and a maybe plottedv from thefollowing data for d: .02.

a. .15 .2 .25 A @316 4373 -.42O .457

ThusEa for a=.25and an approximatelylimit- 'ing peak inverse orforward voltage of '1200 volts,

the highest plate supply voltage permissible wouldbe "Thevalue of aitslfwas chosen as 0.25 because this value fulfill the condition for high frequency operation that 2(1,('12d)e' SiIl. e'"(1'd)'d 0.334 0.434 for (1:025 and :d=.02

If the operating frequency F of 10,000 cycles per second is chosen as being a feasible one and the desired output Pselected is 5000 watts, the constants of .the. circuits may-now be determined.

Thus

R :29123 ohm s "R is .theresistance 'for the conditions that all transformer windings have thesame number of turns .and that all reactors, the .plate voltage supply and the transformer are lossless. Actually, the external value of RL would be reduced to 'make (the "total resistance effective in each mesh have the value'R.

"The ifective value of the output current Ieff .into the load is given by Lis a check, .the vpower .P should .be equal to l cfiR. ]?R=.(23.78) 9.23 5000 watts: check.

. :iilthough 'the embodiment illustratediin Fig.1

ais forta four tube'invertencircuit, -it'willlbe apparen't "that the present invention apr lies :iiequally *wellto a circuit utilizing ithree :or :more Jpairs;.::of .tubes. .As ithe number of .pairs :df'tubes zincrease'd, :however, "the :percentage increase in -max'imum frequency *of operation diminishes. -Finally,:a point will'be reached where'thmaddefd complication and. additional :cost 1 of operation 10f -thesapparatus willmot justify the relatively. small increasein frequency obtained-by adding;another jpairof tubes.

For purposes of illustrating-an embodiment :Of the invention using six tubes, -referenee lie-made to Fig. 3. The principle-of operation is thesame as in the embodiment utilizing four tubes.

In the six tube circuit; there are provided three pairs of gas dischargetubes 3 0and-33,'3l -and -34, and 32 and 35, each tube being provided similar grid circuits and'similarexternal anode to: cathode'circuits. Tubes 30; 3| and 32, which are corresponding tubes of each of the three pairs, are provided withsimilar individual egrid .bias supplies 36, :31rand-38, respectively. Tubes .33, 34 and-35, thecorresponding other tubes-:0! each pair, utilize :thecommon bias .supply 39. which is similar to the other "three bias .supplies. These :bias :supplies furnish a normally high negativebias to the-grids of all=tubes-except whenthe tubes are triggered. The positiveside of atheacommon bias :supply is grounded.

The grid circuits-ofreach rof the tubes.;3l,::;31 33, 34, 35 and 36 are provided with similar grid :current limiting iresistors T40, 4| 42 43, mud

45, respectively.

The output of 'the pulser timing :unit mat shown) is connected to the gridxof .eachtube through the transformers 46,'41,-.48,49,:50 sand *5 I respectively. Thepulsing'operation is exactly the same as in the previously 'described'four-tube tcircuit.

"The-cathodes'of each of the tubes 30,t 3i5sand :32 are connected ito'thepositivaside of "the; grid Lbi'as supplie '36, :31 and 38, respectively. .The tcathodesiof the othertubcs 33,34 and 35v arezconnected to ground.

In the output circuit of the-firstpair of :tubes 30. and 33, there is. provided acommonrcapacito'r 152. Similarly, for each of "the :otherpairs of ftubes23i and 34,. and 32 and .35, there..are"provided eommon capacitors 53 and 54,: respectively.

Theianode circuit of each of the tubes '30,:3l, -32, 33,34and35 isprovided witha similar: induc- .tor 55, 56, 51, 5B, 59 and-lim'respectively.

The outputs of'the three pairs of tubes "appear across a common load resistorG hand arerderived ifrom'v a 'load' transformer havinga single'ssecondary winding 62: and three primary windin'gs'63, 64 and 65. 'Allaprimary windings are woundiinithe sam direction.

The primary winding 63 is common to :the external anode to cathode circuit paths of tubes 30 and 33. 'Iheprimary winding is common to the external anode :tozcathode circuit paths of tubes :31 'and 34. The primary winding is common to the anode to cathodecircuit paths 'of'tubesf32 and 35.

The direct current source or-B supply 66 'has'its positive side-connectedto the anodesof tubes 30, 3| "and 32 and hasits'negativeaside grounded.

The mode of operation-is similardnirprinciple to that described in connection with'the four tubecircuit. The'order offiring of theitubes is 30, 3|, 32, 33, 34 and 35 in sequence. '-"First,:ithe tube 3 31 is fired and .'.the capacitor 52 515 charged.

causing a halt-cycle or output voltage to appear across the load resistor 6|. Next, the tube 3| is triggered, charging the capacitor 53 and causing another half-cycle of voltage of opposite polarity to appear across the load resistor 6|. This is followed by the firing of tube 32 charging capacitor 54 and causing the third half-cycle of output voltage to appear across the load resistor. The polarity of each half-cycle is, in all cases, opposite to the one preceding. Next, tubes 33, 34 and 35 are fired in order, discharging each capacitor 52, 53 and 54, respectively. This causes three more half cycles of output voltage to appear across the load resistor.

Because of the correspondingly longer time permitted each tube for deionization, the cycles may be shortened such that the maximum frequency of operation is twice that possible with the four tube circuit.

There has thus been described a type of inverter circuit utilizing any plurality of gas discharge tubes in multiples of two. It has advantages in simplicity of construction and stability of operation not found in previously known circuits designed for similar purposes and provides for greatly increased frequency of operation at high current outputs. For symmetrical output, the values of corresponding elements in the different circuits should be the same. If symmetrical output is not essential, this requirement need not be adhered to.

I claim as my invention.

In an apparatus for inverting direct current to alternating current, a source of direct current, means for connecting said source to a plurality of gas discharge tubes, said plurality being an 10 even number more than two, external anode to cathode discharge circuit paths for each of said tubes, a capacitor common to the discharge circuits of each two of said tubes, means for coupling said discharge circuit to a common load circuit, said coupling means comprising a transformer having a plurality of primary windings each of which is connected in at least one of said discharge circuits, and including a single secondary winding connected in said load circuit, means for triggering said tubes such that said capacitors are charged and discharged in a predetermined consecutive order from said direct current source, means for halting current flow through a tube before the next tube to be fired is triggered, and means for maintaining each tube in a state in which it cannot conduct current while the other tube having its anode to cathode circuit connected to the same capacitor is conducting.

CHARLES C. SHUMARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,752,247 FitzGerald Mar. 25, 1930 1,891,924 Frink Dec. 27, 1932 1,967,876 Fecker July 24, 1934 1,967,877 Fecker July 24, 1934 1,967,896 Morack July 24, 1934 2,017,708 Bedford Oct. 15, 1935 2,147,474 Wagner et a1 Feb. 14, 1939 2,311,839 Lamm Feb. 23, 1943 

